1. Field of the Invention
The present invention relates to a bit map display apparatus having a hardware-window function.
2. Description of the Related Art
In a recent bit map display apparatus, a display function, called a multiwindow display function, for displaying a plurality of data on a single screen, is required. As one means for realizing the multiwindow display, a hardware-window system by display address control is known. The multiwindow display by the conventional hardware-window system is realized as follows. That is, as shown in FIG. 1, window area 3 is set on an area, which is not normally displayed, of frame memory space 2 larger than display screen 1, and is interrupted on the screen by switching display addresses.
However, in the above system,
(1) High-speed switching of display addresses is necessary.
(2) When a frame memory includes a plurality of planes, the window area is not interrupted on the screen for each plane. Therefore, since the same window area is set for all the planes, this system cannot be utilized for a frame memory having different images in units of planes.